Simple solid rivets with a shaft and a set head are usually used to produce riveted connections between load carrying components of aircraft. The closing or riveted head is formed during mounting by a plastic deformation of the shaft material, for example, by hammering or squeezing. Such solid rivets are conventionally made of alloys of aluminum, titanium or of a nickel-copper forgable alloy. For setting or riveting such a solid rivet it is necessary to carry out working steps on the set head side and on the closing head side namely on the back side of the components to be riveted. Rivet connections produced in this way are, therefore, rather high in labor costs. The need for riveting solid rivets in an automatic manufacturing process could, until now, only be realized for rather simple components, due to the relatively complex working procedures, such as inserting, counterholding, and upsetting.
As opposed to riveting solid rivets, the riveting of so-called blind rivets by automatic riveters poses no problems, since all of several working steps on the back side of a component are not needed for blind rivets. In these blind rivets, the rivet shaft proper is hollow and forms a rivet sleeve. The set head is formed onto the rivet sleeve, whereby a drawing mandrel or shaft with a thickened end is set into the axial through-bore of the sleeve, so that the thickened end is on the closing head side and so that a sufficiently long end of the mandrel extends out of the set head to be gripped by a setting or pulling tool. Such a blind rivet can be set by an automatic rivet machine, whereby the machine guides the rivet, according to a corresponding program, into a predrilled bore until the set head touches the material surface of one of the components to be connected and then pulls the mandrel or shaft into the rivet sleeve. Thus, the thickened end of the mandrel penetrates into a region of the sleeve that extends on the back side of the other component, and widens the remote end of the sleeve opposite the set head, thereby forming the closing head. Upon reaching a specific tensile stress inside the shaft or mandrel, the shaft rips off at a predetermined point, thereby forming the rivet connection. In other versions of known blind rivets the portion of the mandrel or shaft extending out of the set head is removed in an additional working step.
Rivet connections based on conventional blind rivets, such as according to Standard ABS 0219, can be used only for secondary applications or low or no load carrying connections due to a low fatigue strength, since a defined load distribution between sleeve and mandrel cannot be achieved.
The rivet mandrel or shaft of common blind rivets is made of, for example, steel or a suitable nickel alloy, which is, however, rather unfavorable in aircraft construction due to weight reasons. Therefore, rivet mandrels made of aluminum or titanium would be much preferred. It has been shown, however, that these mandrels of aluminum or titanium tend to form cold weldings between the sleeve and the mandrel due to the high friction forces arising during the pulling process between sleeve and mandrel. Therefore, conventional rivet connections of lightweight materials cannot be produced with a consistently reproducible uniform quality and strength. Various solutions to raise the strength factor of blind rivets have become known. Special forms of blind rivets, for example, are known from the Standard NAS 1921. However, such special rivets are rather costly, so that they can be utilized, with respect to their manufacturing costs, only in special cases.
U.S. Pat. No. 3,772,957 (Newton) discloses a self-drilling and sealing rivet in which the rivet sleeve is provided with an enlarged cylindrical bore on its blind end to form a gap, e.g. a cylindrical gap between the inwardly facing surface of the cylindrical bore and the cylindrical surface of the rivet shaft. An adhesive (24) is applied inside the cylindrical gap. The shaft has a drill bit at its free end and the end portion of the drill bit connected to the shaft closes the free end of the sleeve for compressing the adhesive when the shaft is pulled for setting the rivet. The sleeve is provided with holes (28) so that the adhesive may be pressed out through these holes into the seam between the two structural components to be connected by the rivet. This type of structure cannot provide a seal between the set head (20) and the rivet shaft or mandrel, nor between the inner surface of the sleeve and the shaft near the head. The problem of cold welding does not occur, because the shaft and sleeve are made of steel. Rather than forming a cylindrical gap, Newton also shows the formation of two sickle shaped gaps by providing the shaft with an oval cross-section.
U.S. Pat. No. 4,659,268 (Del Mundo et al.) discloses a composite blind fastener in which the sleeve is formed of two concentrical tubes that form together with the mandrel two separate reservoirs for a sealant. One reservoir holds the resin, the other holds the hardener for curing the resin. Initially, the two reservoirs are separated by a fracturable membrane which is destroyed when the blind head is set or upset.
German Patent Publication 2,348,754 (Schruff), published on Apr. 24, 1975, discloses a blind settable threaded pin. The pin is connected to a sleeve, for example, by an adhesive or by a welding.